Nowadays, it is commonly seen that backlight modules are used for electronic devices with flat panel displays, which includes devices as small as hand-held palm pilots and as large as big-screen TVs. A typical backlight consists of a light source, such as Cold Cathode Fluorescent (CCFL) or Light Emitting Diodes (LED), a light guide, a diffuser, and a brightness enhancement film. The design challenge of a backlight module is to generate uniform illumination across the LCD surface and luminance that is high enough to produce good contrast in a day environment (so that you can see the display of a laptop computer or a handheld electronic device, for example, with the room lights on), by the cooperation of the diffuser and the brightness enhancement film. Although, Taiwan is now one of the three major production countries for Notebook PCs, the critical component, backlight modules, still has to be imported and there is a heavy reliance on foreign providers. Thus, it is imperative for Taiwan to establish the design and production technology. Moreover, a conventional backlight usually consists of a plurality of optical films, which is the cause of low luminous efficacy, high manufacture cost and low assembly yield, and so on.
Please refer to FIG. 1, which is a cross-sectional view of a multi-layer brightness enhancement article disclosed in U.S. Pat. No. 6,280,063, entitled “Brightness Enhancement Article”. The brightness enhancement article of FIG. 1 can achieve the objects of collimating and diffusing incident light 14 by respectively forming an array of linear prism 10 having blunted or rounded peaks on the upper surface of the substrate thereof and forming a layer of light scattering protrusions 12 on the lower surface of the substrate thereof, so as to enable a backlight module employing the disclosed brightness enhancement article to generate uniform illumination with increased brightness. However, since the diffusion layer and the collimation layer of the disclosed brightness enhancement article are formed by two separate processes and the incident light 14 is emitting at random after being scattered by the plural light scattering protrusions 12, therefore, there are still space to be improved as to the luminous efficacy and the manufacturing cost.
Please refer to FIG. 2, which is a perspective view of a brightness enhancement film disclosed in U.S. Pat. No. 6,277,471, entitled “Brightness Enhancement Film”. The brightness enhancement film of FIG. 2 has a brightness layer adhesively attached to the top surface of a base thereof, wherein the brightness layer is formed by aligning a plurality of prisms 200 side-by-side in a parallel plane and each prism is formed by aligning a plurality of brightness unit 20 adjacent to one another in a straight line while each brightness unit 20 substantially comprises of curved facet 202 and planar facet 201. The light penetrating the brightness unit 20 is refracted to a region thereby enhancing optical performance in two dimensions. However, the level of skill needed to process and form the geometrical structure of the disclosed brightness enhancement film is high that it is not feasible for mass production.
Therefore, it is in great demand to have an improved optical element capable of overcoming the shortcomings of prior arts.